Welcome to Parasitic Diseases

Environmental Disturbance Leads To Emergence Or Establishment Of Infectious Agents

Irrigation

Fall 2006

ParasiteAny organism that takes metabolic advantage

of another organismVirusesRickettsiaebacteriaFungiProtozoa*Helminths*

Nematodes - round worms Cestodes - segmented flat wormsTrematodes - non-segmented flat worms

Arthropods* - six and eight-legged critters

* Covered in Parasitic Diseases

Required textbook:

Available at bookstore.

$69.95

New England Journal Review of Parasitic Diseases 5th ed.

Helminths (Worms)Nematodes - non-segmented round worms

Cestodes - segmented flat worms

Trematodes - non-segmented flat worms

Nematodes - round wormsNematodes - round worms

1. All are eukaryotes -1. All are eukaryotes - Caenorhabitis elegansCaenorhabitis elegans is theis thebest known example and is free-living in soil.best known example and is free-living in soil.

2. Most nematodes are non-parasitic.2. Most nematodes are non-parasitic.

3. Almost 4 billion people harbor at least one3. Almost 4 billion people harbor at least one species of parasitic nematode. Many havespecies of parasitic nematode. Many have more than one.more than one.

GeohelminthsEnterobius vermicularis Enterobius vermicularis (Pinworm)(Pinworm)

Trichuris trichiura Trichuris trichiura (Whipworm)(Whipworm)

Ascaris lumbricoides Ascaris lumbricoides (Giant intestinal worm)(Giant intestinal worm)

Toxocara canis Toxocara canis and T. and T. cati cati (Visceral larva (Visceral larva migransmigrans))

HookwormsHookwormsAncylostoma duodenaleAncylostoma duodenaleNecator americanusNecator americanus

Strongyloides stercoralis Strongyloides stercoralis (Cochin China diarrhea)(Cochin China diarrhea)

Disability-Adjusted Life Years - DALY (WHO)

Anatomic Site In The Host

Helminths that routinely infect humans

Why so many parasite species??

We live everywhere.We eat everything.In fact,……….

From: Everybody Poops, by Taro Gomi. Kane/Miller Book Publisher, New York

Night Soil

What will it be today?

Reality Check

Immunity and Parasitism

Parasiteantigen

Worm infections elicit Th2 protective immune responses.Protozoan infections elicit Th1 protective immune responses.

Cytokines and Immunity to Parasites

*most important in immune expulsion of protozoa and worms

Enterobius vermicularis (Pinworm)

Helminths: Nematoda

Adult Female Enterobius vermicularis

HeadTail

Ovary with eggs

2 mm

Heavy Infection of Enterobius vermicularis

Photo: Martin Weber, MD, Children’s Hospital; Hannover Medical School; Hannover, Germany

Eggs of Enterobius vermicularis

Unembryonated Embryonated

Larva

Enterobius vermicularis in appendix

Alae

Clinical Disease:

None

Diagnosis:Eggs found on microscopic examination of clearsticky tape.

larva

Drug of Choice:

Mebendazole

Mode of Action:De-polymerizes all species ofinvertebrate tubulins; not vertebratetubulins.

Prevention and Control:

Prevention is difficult amongchildren, especially those attendingday care facilities and lower grades inschool. We “out-grow”our pinworminfections once we reach puberty.

Trichuris trichiura(Whipworm)

Helminths: Nematoda

Female adult Trichuris trichiura

Head

Tail

Adult male Trichuris trichiura

Curved tail

Head

Adult Trichuris muris in situ (SEM)

Pathogenesis:

Trichuris spp. secrete a pore-forming proteinthat may play a role in anemia and diarrhea.Adult worms do not feed directly on blood orother host tissues. Mechanism of anemia stillunknown.

Prolapsed rectum with adultTrichuris trichiura

Trichuris adults

Clinical Disease:

1. Diarrhea

2. Anemia

3. Malnutrition (protein calorie deficiency?)

Diagnosis:Microscopic examination of feces for eggs

25 µm

Fertilized, unembryonated egg

Drug of choice:Mebendazole

Mode of Action:De-polymerizes invertebrate microtubules, only

Prevention and Control:Sanitary disposal of feces

Ascaris lumbricoides(Giant intestinal worm)

Helminths: Nematoda

Adult Ascaris lumbricoides

3 cm

Tail

Head

“Jar-O-Worms”Collected from one rural village in Bangladesh in a single day!

Cross section of adult Ascaris lumbricoides

Larvae of Ascaris lumbricoides in liver

Larvae

Larva of Ascaris lumbricoides in lung

Pathogenesis:

1. “Verminous” pneumonia, lung tissue damage due to migratory larvae.

2. Bowel obstruction - too many adult worms.

3. Parasite secretes trypsin inhibitor, prevents host fromdigesting proteins.

4. Aberrant migration of “irritated” adult worms to:a. Ampula of Vaterb. Common ductc. Liverd. Pharynxe. Peritoneum

Clinical Disease:

1. Light infections are asymptomatic as long as theadult worms do not migrate.

2. Heavy infection leads to:a. protein calorie malnutrition - “failure

to thrive” syndrome.b. bowel obstruction.c. aberrant migratory events.

Child with heavy Ascaris lumbricoides infection

Infant with heavy Ascaris infection

Bolus of Ascaris lumbricoides in small intestine

Ascaris lumbricoides adult in appendix

Ascaris adults in liver (fatal case)

Bolus of Ascaris lumbricoides (fatal case)

Diagnosis:Microscopic examination of feces for eggs

30 µmFertilized, unembryonated egg

Drug of choice:Mebendazole

Mode of Action:De-polymerizes invertebrate microtubules, only

Medical Ecology

Prevention and Control:Sanitary disposal of feces

Toxocara canisToxocara cati

Visceral and ocular larva migrans

Helminths: Nematoda

Adult Toxocara canis

Female

MaleTail

Head

1 cm

Street scene in Paro, Bhutan

Embryonated egg of Toxocara canis

Larva

45 µm

Pathogenesis:

Tissue damage (systemic) due to migratory3rd stage larva

Clinical Disease:

1. Fever

2. Loss of visual acuity

3. Blindness

4. Learning disabilities

Granuloma in retina due to Toxocara canis

Larvae of Toxocara canis in mouse brain

Larvae

Diagnosis:Serological tests (ELISA-based)

Drugs of choice:

Mebendazole

Steroids

Prednisolone

Prevention and Control:Sanitary disposal of dog and cat feces

Not practical

Pooper-scooper

Potty-trained cat!

Prevention and Control (cont’d):2. Periodically de-worm pets.3. Cover public sand boxes at night.